6. Ecosystem evolution and heterogeneity in East Turkana, northern Kenya during Early Pleistocene as indicated by stable carbon and oxygen isotope data from mammalian enamel

Abstract

During the Early Pleistocene of eastern Africa, paleoenvironmental data suggest a shift from wooded-brushland environments to a grassland-dominated landscape more analogous to modern African ecosystems. In this study, we use a large compilation (n=2623) of carbon and oxygen isotope values of both fossil and modern eastern African mammals to investigate dietary evolution and ecosystem dynamics over the past 2 million years in eastern Africa. We find that although most taxa remain isotopically static early in this period (e.g., Reduncini, Hippopotamus), some taxa (e.g., Equus, Alcelaphini) become depleted in their carbon isotopic signature, which indicates an increased prevalence of C3 (i.e., trees and shrubs) vegetation in the diet. These ancient patterns are particularly interesting given that the diet of modern representatives of these taxa is dominated by C4 vegetation (i.e., grasses and sedges). As a case study, we use the isotope values collected from fossil mammals from East Turkana in northern Kenya to assess the degree of habitat heterogeneity during this period. We find that vegetation in this fossil ecosystem was highly variable across space, comparable to that of modern eastern African systems. This study indicates 1) a major restructuring in the African savanna ecosystem, which could be related to increased anthropogenic impacts and 2) both ancient and modern eastern African environments are highly heterogeneous across space. Future studies should expand this dataset to fill important spatial and temporal gaps in the record.